Change "you have custom access"

I have recently set up an early 2015 MacBook Air to use temporarily while my MBP is being repaired. The HD on the MB Air was completely erased and the latest OS installed. I am the Admin and only user. The HD is not partitioned and is formatted APFS, case-sensitive, encrypted.

The problem I have is that some folders (including the home folder (pic) and the desktop folder) have the words "you have custom access" appearing immediately under the sharing and permissions triangle. There is no reason why I (as admin) should have "custom access". I think this may be preventing me from setting up a OneDrive folder on the Mac, but anyway, why does this appear? I tried to change this by unlocking and then adjusting permissions in the drop down menu, but both "make X (me) the owner" and "apply to enclosed items" are grayed out.

I don't know whether this is significant, but normally, isn't the first person in the permissions list marked "Admin"?

As you can see, the first person in the list is [my name, without any spaces], which is the home folder name, and "(me)" after it.

It sort of looks like the permissions list is omitting the administrator altogether.

Hope this makes sense. All help welcome

Thanks

Tom